Catalytic reforming is a well established refining process employed by the petroleum industry for upgrading low-octane hydrocarbons to higher-octane hydrocarbons. Typically, catalytic reforming involves the contacting of a naphtha hydrocarbon feed with a reformer catalyst under elevated temperatures and pressures.
Reformer catalysts typically comprise a metal hydrogen transfer component or components, a halogen component, and a porous inorganic oxide support. A reformer catalyst which has been employed widely throughout the petroleum industry comprises platinum as the metal hydrogen transfer component, chlorine as the halogen component, and alumina as the support. Also, additional metallic promoter components, such as rhenium, iridium, ruthenium, tin, palladium, germanium and the like, have been added to the basic platinum-chlorine-alumina catalyst to create a bimetallic catalyst with improved activity, selectivity, or both.
In a conventional reforming process, a series of two to five reformer reactors constitute the heart of the reformer system. Each reformer reactor is generally provided with a fixed bed or beds of catalyst which receive upflow or downflow feed. Each reactor is provided with a heater because the reactions which take place therein are predominantly endothermic. In a typical commercial reformer, a naphtha feed with a diluent of hydrogen or hydrogen recycled gas is passed through a preheat furnace, then downward through a reformer reactor, and then in sequence through subsequent interstage heaters and reactors connected in series. The product of the last reactor is separated into a liquid fraction and vaporous effluent. The vaporous effluent, a gas rich in hydrogen, may then be used as hydrogen recycled gas in the reforming process.
During operation of a conventional catalytic reformer system, the activity of the reformer catalyst gradually declines over time. There are believed to be several causes of reformer catalyst deactivation, including, (1) formation of coke within the pores, as well as on the surface, of the catalyst, (2) agglomeration of the catalyst metal component or components, and (3) loss of the halogen component. Deactivation of a reformer catalyst can have the following negative impacts on the reforming process: (1) lower product octane number; (2) higher required reaction temperature; (3) higher required reaction pressure; (4) decreased time between required catalyst regeneration (cycle time); (5) increased requirement for hydrogen; and (6) decreased selectivity.
It has been previously recognized that the deactivation of a reformer catalyst can be inhibited by contacting the reformer catalyst with a chloriding agent during reforming. This xe2x80x9cchloridingxe2x80x9d of the reformer catalyst is thought to inhibit catalyst deactivation by (1) counteracting the formation of coke on the catalyst, (2) redispersing the metal component or components of the catalyst in a more uniform manner, and (3) replacing the halogen component which has been stripped from the catalyst during reforming.
The conventional practice of chloriding a reformer catalyst contained in the reformer reactors of a multiple-reactor reformer system is to inject a chloriding agent into the hydrocarbon feed charged to the first reactor of the series. The chloriding agent is then carried with the hydrocarbon feed to the reaction zone of the first reformer reactor and subsequently to the reaction zones of the downstream reactors where it is contacted with the reformer catalyst. An important aspect of the conventional chloriding practice is for the water concentration in the feed to the first reactor of the multiple-reactor reformer system to be maintained and even controlled within a certain concentration range while adding the chloriding agent. This is done in order to keep the water-chloride ratio within the reformer reaction zones at an appropriate level so as to maintain both catalyst activity and stability by suppressing the excessive hydrocracking that is believed to occur during conventional chloriding. The water concentration in the reformer feed is also maintained at certain levels in order to aid in carrying the chloriding agent through the series of reformer reactors so as to properly expose the catalyst contained in the downstream reactors to the chloriding agent.
A disadvantage of conventional reforming methods which require the presence of water in the hydrocarbon feed charged the multiple-reactor reforming system is that water can cause accelerated coking, and thus, accelerated deactivation, of the reformer catalyst. A further disadvantage of requiring the presence of water in the hydrocarbon feed is that water can strip the halogen component from the reformer catalyst causing decreased activity and decreased stability. A still further disadvantage of conventional reforming methods is that the reformer catalyst contained in the downstream reactors of the multiple-reactor reformer system experiences an accelerated rate of deactivation when compared to the reformer catalyst in the upstream reactors of the system, thus decreasing the time between which the entire system must be shut down for regeneration of the reformer catalyst (i.e., decreased cycle time).
It is an object of the present invention to provide an improved reforming process whereby the stability of a reformer catalyst is improved when compared with reforming processes utilizing conventional methods.
It is a further object of this invention to solve problems associated with the use of water as a means for aiding in the conveyance of a chloriding agent from the first reactor of a series of reactors in a multiple-reactor reformer system to the downstream reactors of the series.
It is yet a further object of this invention to provide for the reduction or substantial elimination of water in the feed to the reformer system in order to take advantage of the benefits of processing a dry reformer feed while simultaneously eliminating the disadvantages of processing a dry reformer feed.
A still further object of this invention is to provide for the controlled introduction of a chloriding agent into each of a series of reformer reactors, without the simultaneous introduction of water, in a manner which provides the benefits of the chloriding agent in each of the reactors of the series while realizing the advantages of not having to use water as a carrying aid for the chloriding agent.
An even further advantage of the present invention is that the accelerated rate of deactivation of the reformer catalyst contained in the downstream reactors, versus the upstream reactors, of the multiple-reactor reformer system is counteracted or eliminated, thus decreasing cycle time for the entire system.
Further objects and advantages of the present invention will become apparent from consideration of the detailed description of the invention and appended claims.
Accordingly, in one embodiment of the invention, an improved reforming process is provided in which the stability of the reformer catalyst contained in all the reactors of the multiple-reactor reformer system is significantly improved as compared with other conventional reforming processes. This improved reforming process includes charging a substantially water-free reformer feed comprising a reformable hydrocarbon to a reformer system comprising at least two reactors serially connected in fluid-flow communication, with each reactor containing at least a volume of reformer catalyst and operating under reforming conditions. While the substantially water-free reformer feed is being charged to the multiple-reactor reformer system, a chloriding agent is introduced, without simultaneously introducing water, immediately upstream from the inlets of all the reformer reactors in an amount and for a period of time that is effective to inhibit the deactivation of the reformer catalyst. The introduction of the chloriding agent into all the reformer reactors of the multiple-reactor reformer system must occur sequentially, with only one reactor at a time receiving an injection of the chloriding agent.
In another embodiment of the invention, the deactivation of a reformer catalyst of a reformer system comprising an initial reactor, at least one intermediate reactor, and a final reactor serially connected in fluid-flow communication is inhibited or counteracted by charging a substantially water-free hydrocarbon feed to the reformer system while operating under reforming conditions. While the substantially water-free hydrocarbon feed is being charged to the reformer system, a chloriding agent is introduced, without the simultaneous introduction of water, into the inlet of each of the initial reactor, the intermediate reactor or reactors, and the final reactor in an amount and for a time period that are effective to inhibit the deactivation of the reformer catalyst. The introduction of the chloriding agent into the initial reactor, the intermediate reactor or reactors, and the final reactor must occur sequentially, with only one reactor at a time receiving an injection of the chloriding agent.
A still further embodiment of the invention includes a method of operating a reformer system that has a first reactor, a second reactor, and a third reactor. The first reactor has a first inlet for receiving a feed and a first outlet for discharging a first effluent and defines a first volume containing a first catalyst. The second reactor has a second inlet for receiving a first effluent and a second outlet for discharging a second effluent and defines the second volume containing a second catalyst. The third reactor has a third inlet for receiving the second effluent and a third outlet for discharging a third effluent and defines a third volume containing a third catalyst. A first conduit means is operatively connected to the first inlet and provides for conveying the feed to the first reactor. A second conduit means is operatively connected to the first outlet and the second inlet and provides for fluid-flow communication between the first reactor and the second reactor and for the conveyance of the first effluent from the first reactor to the second reactor. A third conduit means is operatively connected to the second outlet and the third inlet and provides for fluid-flow communication between the second reactor and the third reactor and for the conveyance of the second effluent from the second reactor to the third reactor. A fourth conduit means is operatively connected to the third outlet which provides for conveyance of the third effluent from the third reactor. The inventive method includes charging a substantially water-free hydrocarbon feed comprising a reformable hydrocarbon to the reformer system that is operated under reforming conditions through the first conduit means. Simultaneously with the charging step, a chloriding agent is introduced into the first conduit means without the simultaneous introduction of water in an amount sufficient to provide a concentration of the chloriding agent in the substantially water-free hydrocarbon feed in the range of from about 0.1 ppmw to about 10 ppmw. Thereafter, simultaneously with the charging step, the introduction of the chloriding agent into the first conduit means is terminated. Thereafter, simultaneously with the charging step, a chloriding agent is introduced into the second conduit means without the simultaneous introduction of water in an amount sufficient to provide a concentration of the chloriding agent in the substantially water-free hydrocarbon feed in the range of from about 0.1 ppmw to about 10 ppmw. Thereafter, simultaneously with the charging step, the introduction of the chloriding agent into the second conduit means is terminated. Thereafter, simultaneously with the charging step, a chloriding agent is introduced into the third conduit means without the simultaneous introduction of water in an amount sufficient to provide a concentration of the chloriding agent in the substantially water-free hydrocarbon feed in the range of from about 0.1 ppmw to about 10 ppmw. Thereafter, simultaneously with the charging step, the introduction of the chloriding agent into the third conduit means is terminated.